Sensors for recognizing moisture on a glass pane of a motor vehicle are discussed, for example from German Patent No. 199 33 640, but these sensors may be very large because of their complex, optical elements. Since the optical elements must be situated on the windshield of the motor vehicle in the region swept by the wiper, and are consequently in the visual range of the driver, the appropriate casing may distract the driver. This applies in particular because the relatively large casings require complex fixing elements, which are additionally provided on the glass pane. This may be complex and may be very costly in the series production.
A holographic sensor for recognizing drops of water on a glass pane is discussed in European Patent Application No. 999 104. In this reference, a hologram film is glued to or into the windshield.